The login redirect page uses the following hooks:
Code:
init_startup
cache_permissions
style_fetch
cache_templates
global_start
parse_templates
fetch_musername
notices_check_start
notices_noticebit
global_setup_complete
login_verify_success
fetch_userinfo_query
fetch_userinfo
login_process
login_redirect
redirect_generic
I'ma guess you'd use login_process or fetch_userinfo_query and just do an if statement that executes a query to grab the IP and compare.
If you want maximum security, remember to use .htaccess on mod and admincp dir's, rename the dir's to random strings and never chmod anything 777 (although as an owner of a large MMORPG forum I'd guess you know most of this).
I wouldn't recommend hashing your IP address.. for a few reasons. The main one being it's just added load for your server which is unnecessary.